Hardware enforced virtual sequentiality

Abstract

A mechanism processes memory reads and writes in a packet processor. Each memory access has an associated sequence number and information is maintained allowing the detection of memory conflicts. The mechanism is placed between a processing element and a memory system such that write data is buffered and both reads and writes are recorded. When a memory conflict is detected, based on a strict or alternate ordering model, a restart signal is generated and the entries for the associated sequence number are flushed. When the work associated with a sequence number has completed, a signal is made so that associated write data can be sent to the memory system and the entries for that sequence number can be flushed.

1. A method of processing memory reads and writes in a packet processor comprising the steps of:
 receiving a memory read having a first associated sequence number; 
 receiving a memory write having a second associated sequence number; 
 determining if a memory conflict exists between said memory read and said memory write based on a comparison of said first associated sequence number and said second associated sequence number; and 
 signaling a restart based on said step of determining, utilizing said first associated sequence number. 
 
     
     
       2. The method of  claim 1  wherein said step of receiving a memory read comprises the steps of:
 recording a first address and said first associated sequence number in a read table; 
 searching a write table for an entry with an address matching said first address and a sequence number equal to or less than said first associated sequence number; 
 if said step of searching succeeds, retrieving data from said write table. 
 
     
     
       3. The method of  claim 2  wherein said step of receiving a memory write comprises the step of:
 recording a second address, said second associated sequence number and write data in said write table; 
 and wherein said step of determining if a memory conflict exists comprises the step of:
 searching said read table for an entry with an address matching said second address and a sequence number greater than said second associated sequence number the received memory write. 
 
 
     
     
       4. The method of  claim 3  further comprising the step of:
 receiving a start signal with a third associated sequence number; and 
 receiving a done signal with a fourth associated sequence number; 
 wherein a list of active sequence numbers is maintained. 
 
     
     
       5. The method of  claim 4  further comprising the steps of:
 sending write data to a memory system upon receipt of said done signal; 
 flushing the entries in said read table and said write table corresponding to said fourth associated sequence number.